> . I •
U.S. DEPARTMENT OF AGRICULTURE,
BUREAU OF ENTOMOLOGY CIRCULAR No. 17*
U O MOM AKI>. I ninmolosi.i iad ( h.n ol Bnu
ARSENATE OF LEAD AS AN INSECTICIDE
AGAINST THE TOBACCO HORNWORMS.
BT
A. C. MORGAN \m> D. C. PARMAX,
Entomtlofical Assistant*.
M047*— 18
.TON ; OOVMNMtST mihTINO Of'ICt '•'!
BUREAU OF ENTOMOLOGY.
L. O. Howard, Entomologist and Chief of Bureau.
C. L. Marlatt, Entomologist and Acting Chief in Absence of Chief.
R. S. Clifton, Executive Assistant.
W. F. Tastet, Chief Clerk.
F. H. Chittenden, in charge of truck crop and stored product insect investigations.
A. D. Hopkins, in charge of forest insect investigations.
W. D. Hunter, in charge of southern field crop insect investigations.
F. M. Webster, in charge of cereal and forage insect investigations.
A. L. Quaintance, in charge of deciduous fruit insect investigations.
E. F. Phillips, in charge of bee culture.
D. M. Rogers, in charge of preventing spread of moths, field work.
Rolla P. Currie, in charge of editorial work.
Mabel Colcord, in charge of library.
Southern Field Crop Insect Investigations.
W. D. Hunter, in charge.
W. D. Pierce, J. D. Mitchell, G. D. Smith, E. A. McGregor, Harry Pinkus.
B. R. Coad, W. A. Thomas, R. W. Moreland, A. W. Jobbins-Pomeroy, C. E.
Hester, engaged in cotton-boll weevil investigations.
A. C. Morgan, G. A. Runner, S. E. Crumb, D. C. Parman, engaged in tobacco
insect investigations.
F. C. Bishopp, A. H. Jennings, H. P. Wood, W. V. King, engaged in tick investi-
tions.
T. E. Holloway, E. R. Barber, engaged in sugar-cane insect investigations.
J. L. Webb,' engaged in rice insect investigations.
R. A. Cooley, D. L. Van Dine, A. F. Conradi, C. C. Krumbhaab, collaborators.
(ii)
fci
Circular No. 173.
United States Department of Agriculture,
BUREAU OF ENTOMOLOGY.
L. O. HOWARD, Entomologiat and Chief of Bureau.
ARSENATF, OF LEAD AS AN INSECTICIDE AGAINST THE
TOBACCO BOBNWORMS.
By A. <". MnwiAN :md I). C. I'armaN,
Entomological AltistOntt.
IN TKODUCTOKY.
During the past five years the Bureau of Entomology has been
conducting an investigation of tobacco insects in Tennessee and
Kentucky and in some of the adjoining States. In Tennessee the
bureau has been very materially assisted by Prof. H. A. Morgan,
director of the Tennessee Agricultural Experiment Station.
In the dark-tobacco districts of Kentucky and Tennessee tobacco
hornworms are the ever-present and most serious problem of the
tobacco grower, Ten to twelve years ago, when labor was plentiful,
•heap, and efficient, "hand-worming" was found to be economical
and effective in combating this pest However, during the last six or
eight years hand-worming has become too costly, because of the
ivity of labor, and too inefficient, and the growers have been
forced to employ an insecticide. At the time insecticides were first
used Paris green was found to be the safest and most efficient. Nev-
ertheless, there has always l>oen complaint of frequent serious burn-
ing of tobacco as a result of its use. To find a safe and effective
insecticide has been one of the main lines of investigation by the
writers during the past five years. Di-plunihic arsenate of lead has
been found to meet the requirements. In the further discussion of
this subject the use and action of Pari- green will be rather thor-
oughly discussed in connection with the use and action of arsenate
of lead, for the reason that since the insecticida] results of the use of
green are so well known it will be easier to explain the value
of arsenate of lead if it be compared with this well-known poison.
1
J
2 ARSENATE OF LEAD AGAINST TOBACCO HOKNWORMS.
NECESSITY AND ADVANTAGES OF THE USE OF AN INSECTICIDE.
The way in which the scarcity of labor tended to bring about the
use of an insecticide upon tobacco has already been explained. In
addition to this necessity of using insecticides, the much greater
efficiency of a good application of an insecticide is another strong
argument in its favor. Hand-worming, even of the best, has many
objections; for instance, eggs are not picked off, many small worms
are overlooked on account of their small size, and, lastly, during the
hot hours of the day large worms crawl down into the " ruffles " near
the bases of the leaves and a considerable number are thus over-
looked. On the other hand, a thorough application of an insecti-
cide will kill practically every hornworm — except those very nearly
full grown — within two or three days, and will also continue to kill
the young worms that hatch several days after the application. In
short, hand-picking has only an immediate effect in lessening the
worms, whereas the application of an insecticide usually continues to
kill over a period of several days. Cheapness is another point very
greatly in favor of an insecticide as compared with hand-picking.
The cost of keeping an acre of tobacco hand-wormed in a year when
worms are plentiful is variously estimated at from $6 to $10. A like
number of worms can be killed with an insecticide at a cost of not
more than $2 or $3 an acre — sometimes less.
THE USE OF PARIS GREEN.
In some districts of Kentucky Paris green has been in use for over
a decade. In the dark-tobacco districts of Kentucky and Tennessee
it certainly was used to some extent 10 years ago and at the present
time is in very general use. On account of the frequent injury to
tobacco by the use of this insecticide many farmers would not use it
if labor could be secured to do the hand-picking. On the whole, the
cost of the Paris green plus the cost of application, plus the loss
due to damaged tobacco, is much less than the cost of hand-worming.
In this district the use of insecticides has come to stay. It is a neces-
sity.
Paris green is applied with a dust gun and without a carrier.
From 1 to 2 pounds per acre is the usual application; 1 pound when
worms are small (i. e., less than half grown) and 2 pounds when
there are many worms over half grown. Success with the applica-
tion depends upon the judgment of the farmer in choosing the time
of application and upon the thoroughness with which the application
is made. Much of the tobacco that is injured by Paris green is in-
jured because of unevenness of application, or. what is too frequently
the case, because the grower has delayed the application until half-
IB8SNATB 01 LEAD LQAIN81 N>BACG0 HOBNWOBM 8
grown or two-third- ^rmvn worms haw become dangerously nn-
merous, and has then put <»n a large and uneven application with the
bope thai he would kill all the large worms. Thia is an example of
poor judgment. Two applications Bhouid have been made. '1 l> •
first should have been smaller and at an earlier date in order to kill
the worm- while small, and also to lessen the danger of burning the
tobacco. The second application should follow as soon as. worms
ii to increase in numbers after the first application.
OBJECTIONS TO TH] PS] 01 PABIS QB1 i n .
DA1TOI B K) T1IK OH KOOIi.
There is occasionally Borne injury or irritation to the operator in
applying Paris green. Wherever Paris green strikes the tender
parts of the body irritation soon occurs unless a thorough bath be
taken promptly, Bleeding at the uose sometimes occurs as ■ result of
the irritation to the mucous membranes, For these reasons many
people dislike to apply Paris green. However, if care is taken to
work in a direction quartering the breeze and upon the windward
Bide of the row while making an application, a thick sack around
the body and a sponge over the UOSC will be found to he excellent
preventives of irritation, particularly if followed by a hath.
IN.ICKY BY PABIS (iBK.KN TO TOBACCO.
The very general complaint of loss d\n' to Pan- green-burned to-
bacOO has been found to be justified. Under favorable weather con-
dition- 9 pounds of Pari- green per acre, sometimes more, may be
applied without noticeable injury. On the other hand, unfavorable
weather condition- will frequently cause injury to follow an appli-
cation of only 1 pound per acre. Very hot -uns and low humidity
for an extended period will produce a condition of the tobacco plant
very susceptible to Paris-green bum. Light rains or very heavy
.lews immediately following an application will wash the Pan- green
down into the axil- of the leaves or into the furrows along the mid-
ribs, and serious injury i- likely to result.
In the Clarksville district of the dark-tobacco belt of Kentucky
and Tennessee Paris-green burn was quite severe during l'.'ll and
1912, particularly so in L912. Previous to these years one of the
most careful growers in this district informed the writers that his
I..-- on a 6-acre field of tobacco, due to Palis-green burn, amounted
lo 8 per cent gross, which WSS a lo-- of at lea-t If. per cent of the net
profit, and that many other growers suffered a similar lo-- in 1912.
In 1911 the writer.- observed many fields in which the loss equaled
or exceeded that quoted above. In L912, however, the injury by Paris
green was more widespread than for several year-, notwithstanding
i
4 ARSENATE OF LEAD AGAINST TOBACCO HORN WORMS.
the fact that many growers who suffered loss the year before were
extremely careful in making applications.
On January 4, 1913, the senior writer interviewed several tobacco
buyers employed by the Italian Government. He was informed that
several crops of tobacco the grade of which was especially suitable
for the Italian Government were not bid upon because of the large
percentage of tobacco injured by Paris green. The buyer stated that
for one crop, had it been in average condition in regard to Paris-
green injury, he would have bid 8^ cents per pound. In its damaged
condition, however, he did not believe the crop was worth over 5
cents per pound — a gross loss of 3^ cents per pound, or of $25 to $30
per acre. Another crop would have received an offer of 8 cents per
pound from the Italian buyers, but on account of Paris-green burn no
offer was made. This buyer thought the crop worth not more than
5| cents — a gross loss of 2^ cents per pound, or about $20 per acre.
A third crop had its value reduced by one-half, a fourth crop was
apparently worth about 5 cents per pound, and would ordinarily have
brought 9 cents. This is the report of buyers of the heavier types of
tobacco grown in this district. The lighter-bodied tobaccos undoubt-
edly suffered as severely and probably more severely than the heavier
tobaccos, because the lighter tobaccos are ordinarily more susceptible
to Paris-green injury.
Paris green injures tobacco in two ways: First, by causing dead,
burned areas upon the leaves, where the powder has been collected by
the dews or washed down by the rains; second, by weakening the leaf
at the stalk. Light rains wash the insecticide into the axils of the
leaves, and the result is that many leaves drop off before cutting time
or become so weakened that they drop off when the plant is cut.
Such leaves are not a total loss, for they are collected and cured, but
they are a partial loss. They are light in weight and lack gloss and
elasticity.
THE USE OF ARSENATE OF LEAD.
Arsenate of lead causes none of the injury mentioned above. Ex-
periments performed under the direction of the senior writer showed
that powdered arsenate of lead may be put on a fresh sucker wound
in large quantities without causing any noticeable injury, and that
when applied to a torn or bruised leaf it produces no injury. Paris
green can not be applied to tobacco in the "graining" stage (i. e..
when nearly ripe) in sufficient quantities to do good insecticidal work
without too grave danger of burning the plant. Arsenate of lead, on
the other hand, can be safely applied to tobacco in the " graining "
stage in quantities sufficient to produce satisfactory insecticidal re-
sults. Furthermore, arsenate of lead will cause no irritation to the
ARSENATE 0] LEAD A0AIN81 rOBACCO BOBNWOBM8.
operator as will Puis green; in feet, thus far it bee produced do
Doticeable injurious effects upon the operators.
Since arsenate of lead can be applied t" tobacco without injuring
Hie plant, and since it i> very much lees objectionable from tin- oper
■tor's standpoint, its insecticide! properties Bhould next !>»■ disci
A-. the dosage end action <>f Paris green arc irerj widely known, the
value of arsenate ol lead as an in secti cide can the more easily In*
explained by comparing it with Pans green. I In- following tables
will serve t'> Bhos the relative values of the two insecticides under
different conditions.
Tabli I.- Comparison of fAe Insecticidal effects against horweortns of arsenate
of lead and Parte grean In f'ii> w athi
I 'ile of
ftppU ttkn
s
B.d
o »
2
a
3
V.
Poison used.
K summations to (hem number ol worm- killed.
3
o
V.
g
-
a
On day
-'1-
pttad.
On flm
day
alter.
and
day
after,
On
third
on
fourth
after
on
Oftb
day
;ifl>T.
5 .
'ft'S
„1
°a
1
E
=
2
d
>
<
1
a
d
>
<
1
Q
d
■o
•:
>
<
1
d
<
d
-
d
<
a
1
".1910
Aiu- J4 19111
1 1911
1,1911
s
1
I-ead arsenate.
Paris green.
Paris green
134
130
106
135
107
5
7
40
7.1
h
80
56
61
49
45
17
M
35
14
70
61
29
SI
17
30
lo
'14
50
3
5
35
50
:
23
15
(»)
(»)
50
4
31
i
100
s
100
1 Taken on 200 plants by ordinary band-worming.
> Uiuiy small worms alire.
Arsenate-of-lead experiments Nos. 1 and 2 wen 1 applied under
Very favorable conditions, i. e., there was dew upon the plants and
do breeze. Paris-green application No. 3 was applied under equally
favorable conditions. These three experiments killed worms very
satisfactorily. The records in Table I were made by counting the
worms on 60 plants of tobacco on each succeeding day after the ap-
plication. No. 1, 5-pound dosage of arsenate of lead, gave th>-
best results, for on the fourth day after the application only 2 live
worms were found in hand-worming 200 hills. The 3J-pound dosage
of arsenate of lead was not quite so good, although only 14 live worms
were found on 200 plants the fourth day after the application. The
Paris-green application No. 3 killed more quickly than either of the
applications of arsenate of lead, but on the fifth day after the appli-
cation numerous small worms were noticed in worming 200 plants.
It was thus apparent that the Paris green was losing it> effect, owing
to heavy dews which tended to puddle it. and to heavy drying winds
during the day. which blew some of it from the plants.
The application in experiment No. 4 was not made under the nm-i
favorable conditions. There was a slight breeze during the appli-
J
G
ARSENATE OF LEAD AGAINST TOBACCO HORN WORMS.
cation; in addition, there were a large number of eggs on the plants,
and many of the young worms hatching from these eggs were not
killed until they wandered from the place of hatching. The same
is true of experiment No. 5, the lf-pound dosage of Paris green. It
will be seen, however, that experiment No. 4, the arsenate-of-lead
application, was more effective than the Paris-green application, for
on the day of application there were at least 140 worms in experi-
ment No. 4, the arsenate-of-lead application, and only 114 worms in
experiment No. 5, the Paris-green application, while on the fourth
day after the applications there were only 31 live worms in experi-
ment No. 4, but 52 in experiment No. 5.
The poisons were applied in the following series of tests in the
morning from 6.30 to 9 o'clock. The arsenate of lead was mixed with
an equal weight of dry wood ashes. All applications were made with
fan dust guns. The mixture of ashes and lead arsenate made a very
good dust and compared favorably in evenness with the application
of Paris green. Rain began to fall at 11.30 a. m. and continued in-
termittently until 2 p. m. Part of the rain was dashing. About one-
third of an inch fell. The first examination of the plats was made
after 3 p. m. of the same day. The tobacco on these plats was nearly
full grown and lapped in the rows considerably.
Table II. — A comparison of the iiixvcticidal effects against hornworms of
arsenate of lead and Paris green in rainy weather.
Date of
application.
Dosage.
Poison used.
Examinations to show number of worms
killed.
6
a
a
On day
applied.
On first
day
after.
On
second
day
after.
On On
third fourth
day day
after. 1 after.
Size of
worms left.
g
R
>
<
OS
o
a
d
>
<
•o
8
a
>
<
a
©
>
<
■a 9
a .C
a —
O <
3
a
1
Auk. 2R.1911
do
do
Pound*
ptracrf.
5
4
2J
Lead arsenate.
do
59
102
87
49
21
15
15
4S
54
41
27
29
10
21
34
8
13
14
6
33
36
2
8
9
Small.
2
Small and
3
Paris green
medium.
Small to
large.
The three experiments recorded in Table II are very interesting.
They show, first, that arsenate of lead was far more effective during
rainy weather than was Paris green (see number of live worms on
the fourth day), even though a very heavy dosage of Paris green
was used; second, that to be very effective during rainy weather an
application of at least 5 pounds of arsenate of lead per acre is re-
ARSI \ u I "I LEAD IGAINS1 rOBACCO HORN WORMS. 7
quired. Experiment No. ■_'. I pounds of arsenate of lead per acre,
more affective than the -'. pounda of Piris green. AJthough a
oonaidefable Dumber of worms were left on plat B, we Bnd thai fewer
were alive in this experiment on the fourth day than were slive in
the Paris green experiment, notwithstanding the fad that there weir
practically 20 per cent more worms on No. B, the arsenate of lead
plat, at the time of application of the poison than there were mi the
Pari- green plat. Fortunately for the effect upon the tobacco plants,
the rain washed off nearly all the Paris green, so that there was eery
little burning. There was do burning of plant- on the arsenate of
lead plats.
Tun i- in. CotHpOfiwK of tnaectMSol effect "f pood mill poor application* i>f
111 N- miti nj b ad.
Dateof appti-
lon.
-
c
8
KxniuiimiiutLs to Bad numbef of worms
killed.
6
M
-
Day
ap-
pltod.
i M
after.
■li v
Thinl
after
M
!
£
>
5
—
■d
«J
—
-
3
\
1
Aug. 16,1910
Aug. 25,1910
4
31
33
N
61
41
35
u
e-
11
I. Ill" -i pUllls
■ 50 plants
(•our.
2
• U
i
On
201
pla
n!-^.
Ill T;»l>le III. which gives a comparison Of S good and I poor ap-
plication of arsenate of lead, application \o. l. 41 pounds arsenate
of lead per acre, was from the sump keg as application No. 2, •"•',
pounda per acre. Counts were made on .">() hills in each instance.
On Augu-t 10, IB10, many eggs were noticed on the plants, 90 that
most of the worms appearing on this plat were small. It will be
noticed that the application did not keep down the increase of WOlTOS
due to hatching. In experiment No. 2 there were very few eggs "ii
the plants and the worms were therefore larger than on plat 1 and
harder to kill. Practically a clean sweep was made on No. •_'. only
1 [ worms heing found on 200 plants on the fourth day after the
application. Favorable weather prevailed after both applications,
and the conditions at the time of application to both plats were
equally favorable. What. then, is the explanation of the poor results
on plat 1 and of the very excellent results on plat •-' *. The explana-
tion is found in the carrier. In No. 1 the arsenate of lead WBS mixed
thoroughly with an equal weight of finely sifted air-slaked lime,
while in No. 2 it was thoroughly mixed with an equal weight of
finely sifted dry wood ashes. Notwithstanding the dryness of the
A
8 AB6ENATE OF LEAD AGAINST TOBACCO HORNWOBMS.
lime the mixture lumped out of the gun considerably. On the other
hand, the arsenate of lead and ashes made a very even dust, with
scarcely any lumping. These two experiments are here shown to
emphasize the necessity of applying a thoroughly even dust. A
lumpy application is a waste of time and material and will be no
more effective than would a perfect application which had been
rained upon immediately following the application.
HOW TO APPLY ARSENATE OF LEAD TO TOBACCO.
Paris green is generally applied to tobacco by means of a dust
gun and without the admixture of a carrier. On the other hand,
arsenate of lead must be mixed with a carrier in order to secure an
even and thorough distribution. Several carriers have been tested
with this insecticide. Finely sifted air-slaked lime, to our surprise,
did not dust evenly. Road dust and land plaster proved to be too
heavy. The best results were obtained with finely sifted, freshly burned
wood ashes. At least an equal bulk of the wood ashes should be used.
Mix the arsenate of lead and ashes very thorough]}' and apply while
there is dew upon the tobacco and when there is no breeze. Even if
very dry and finely sifted ashes are used, unsatisfactory results will
be obtained unless the application is made with a powerful dust gun.
The hand-power dust guns now in general use do not furnish suffi-
cient power to make anything like a satisfactory and effective appli-
cation. Special guns that will perform satisfactory work are gradu-
ally coming on the market. The new guns have a fan with a diame-
ter of 8 inches, whereas the old guns have a fan diameter of only 6
inches. The new guns have also an auxiliary dust chamber, which
is very essential, because the dust containers of the old guns are so
small that they have to be refilled five or six times for each acre
dusted. Two refillings of the new guns will be sufficient for dusting
an acre.
To secure the best results dust the tobacco when dew is upon the
plants and when there is no breeze. By reference to Table III we
see the comparative results of a good and a poor application of
arsenate of lead. The use of a carrier that does not dust evenly, the
application of the insecticide when there is too much breeze, and the
use of too small a dust gun are all certain to give unsatisfactory
results. Avoid these mistakes, and satisfactory results will be secured.
Thoroughness of application can not be too strongly recommended.
When tobacco worms are numerous a poor application of an insecti-
cide will miss worms enough to ruin in two days more than enough
tobacco to pay for the whole application. Make the application
thorough.
LRSENAT] .'I LEAD \..\l\si rOBACCO B0BNW0RM8. B
ran qrao] or umnui 01 1 1 vD 10 t n loainsi red pobao
BORN Hi, UU,
\r 1 1 ,: if lead, theoretically, ere either triplumbic or diplumbic,
although many of tlic grades and brands are undoubtedly a mixture
of the (\\<>. Numerous experiments by agents of the bureau I iu \ ••
proved thai triplumbic arsenate of lead is a very unsatisfactory
insecticide for use against tobacco bornworms; in fact the in
ridal action of thi> grade is bo slow that ?erj few growers would
p( an application as ;i gift. On the other hand, an arsenate of
lead composed almosl entirely of the diplumbic form produces very
satisfactory insecticidaJ results when used against this insect.
In both the triplumbic and diplumbic forms the arsenic i-. present
as arsenic acid. Theoretically triplumbic arsenate of lead in pow-
dered form contains 25.58 per cent of arsenic acid, while the diplum-
bic, in powdered form, contains theoretically 88.15 per cent of
arsenic acid. Tobacco growers should demand a powdered arsenate
of lead that is composed largely of the diplumbic form. In order to
be certain that the diplumbic form is predominant buy only those
powdered arsenates of lead which the manufacturers will guarantee
to contain at least :W per cent of arsenic acid: also insist upon a
guaranty of not more than 1 per cent of free, or water-soluble, arseni-
OUS acid, in order to he sure that the applications will not burn the
tobacco. The writers advise growers and dealers who may use or
handle powdered arsenate of lead for use against tobacco worms to
demand a written guaranty that the composition of the products is
as recommended above.
WHEN TO APPLY ARSENATE OF LEAD.
The first application of arsenate of lead should be made when
tobacco worms become too numerous to be kept off tobacco by the
hand-picking that is usually done while hoeing, Buckering, or topping
tobacco. In some years B BOCOnd and even a third application may
be necessary. The time for making these applications will be indi-
cated by the numbers of eggs and young worm- appearing on the
tobacco.
\GK. OK ARSENATE OF LEAD RK.QIIRK.I).
When tobacco is small and has not begun to lap in the row an
application of 8J pounds of arsenate of lead per acre will be efficient.
Full-grown tobacco should receive not Less than 5 pounds per acre.
In water spray use 8 to 4 pounds of powdered arsenate of lead per
100 gaUons of water.
A
10 ARSENATE OF LEAD AGAINST TOBACCO IKiKXWOEMS.
COST OF ARSENATE OF I.KAI).
The special grade of powdered arsenate of lead recommended for
use on tobacco will cost about 22 cents per pound at the factory in
100-pound kegs. The freight will be about 1 cent per pound, mak-
ing the total cost 23 cents per pound to the grower. Therefore a 3£-
pound dosage will cost about SO cents, while a 5-pound dosage will
cost $1.15. A 2-pound dosage of Paris green costs from 50 to 55
cents, while a dosage of 1] pounds, which is the smallest which should
be applied, will cost about 31 to 35 cents. If the comparative cost
of Paris green and arsenate of lead were the only question to be con-
sidered, it would be useless to recommend arsenate of lead. The
cost, however, for the careful grower should be a matter of strictly
secondary consideration. The certainty of not burning the tobacco
should more than compensate for the extra cost of this insecticide.
SUMMARY.
Paris green frequently burns tobacco very severely, and may
reduce the value of the crop as much as 50 per cent in exceptional
cases.
It is impossible to apply an effective dosage of Paris green without
risk of burning tobacco.
Paris green, which is applied in dust form, is used at a dosage of
from 1 to 2 pounds per acre.
Arsenate of lead is safe and effective during rainy weather, while
Paris green is dangerous and ineffective.
It is recommended that arsenate of lead be used against the tobacco
hornworms, and that it be applied as a dust or powder.
The dosage of arsenate of lead in powdered form varies from 3$
pounds per acre to 5 pounds per acre. If applied as a spray, use 3
to 4 pounds in 100 gallons of water.
Arsenate of lead applied in powdered form, as here recommended,
must be mixed with a carrier. The best carrier found so far is dry
wood ashes, used in a bulk at least equal to the arsenate of lead.
In applying arsenate of lead use a dust gun having a fan diameter
of at least 8 inches.
Apply arsenate of lead when there is no breeze and when dew is
on the plants.
Approved :
James Wilson.
Secretary of Agriculture.
Washington, D. C, February (J. 1913.
ADDITIONAL COPIES of this publication
A may be procured from the Supebinteniv
ent of Documents, Government Printing
Office, Washington, D. C. , at 5 cents per copy
»
1
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